Doom 64 starts where all the other Doom games ended. The lone surviving Space Marine thought it had finished dealing with demons, but one managed to reanimate its fallen comrades for a final push.
The game is quite different from the original; it features new monster sprites, textures, and effects like pseudo-3D environments and custom scripting. This allows for unique things like changing levels and item spawning.
There are 32 levels in total, including special "fun" levels that can't be accessed during normal gameplay.
The enemy lineup is similar to Doom II , but with a few new additions, such as the "nightmare imp", which moves faster than usual. The end boss has also changed and can be defeated using the Unmaker weapon.
The game's atmosphere is darker than before, partly because of the new soundtrack, featuring creepy ambient sounds instead of classic metal tunes.